Mr. and Mrs. Frank are planning to conceive a child and are interested in receiving genetic counseling because of their ages and a history of cystic fibrosis on Mrs. Frank's side of the family. A brief history reveals that Mr. Frank has no known family history of cystic fibrosis or any other genetic disorder. He is 45 years old and has two children from a previous marriage, both of whom are well. Mrs. Frank has a sister with three children the last of whom was diagnosed with cystic fibrosis. There are no other known family members with this disease. Mrs. Frank is 35 years old and has no children. When assessing the risk for bearing a child with cystic fibrosis, one must consider that the disease is genetically inherited as:

A. autosomal dominant
B. autosomal recessive
C. X linked
D. Chromosomal